A process for producing a rigid foamed synthetic resin (hereinafter sometimes referred to as “rigid foam” by reacting a polyol component with a polyisocyanate component in the presence of a blowing agent, a foam stabilizer and a catalyst, has been widely practiced. Among various rigid foams, a rigid isocyanurate foam is excellent in heat insulating properties and flame retardancy and has high strength, and it is accordingly suitably used for building material panels, etc.
As a blowing agent to be used for the process for producing such a rigid isocyanurate foam, a chlorinated fluorocarbon compound (a CFC compound) such as a chlorofluorocarbon compound or CCl3F; or a chlorinated fluorohydrocarbon compound (a HCFC compound) such as a hydrochlorofluorocarbon compound or CCl2FCH3 has, for example, been used.
However, the CFC compound and the HCFC compound have such a problem that their use is restricted from the viewpoint of environmental protection.
As a blowing agent to replace such restricted compounds, it has been studied to use a hydrocarbon compound such as cyclopentane, a fluorohydrocarbon compound (a HFC compound) such as a hydrofluorocarbon compound, or water.
The HFC compound may, for example, be CF3CH2F (HFC-134a, boiling point: −27° C.), CF3CH2CHF2 (HFC-245fa, boiling point: 15° C.) or CF3CH2CF2CH3 (HFC-365mfc, boiling point: 40° C.).
However, the HFC compound has a high global warming potential and thus is still problematic from the viewpoint of environmental protection, and a study is being made to use, as a blowing agent, a hydrocarbon compound or water which has a low global warming potential.
In a case where a hydrocarbon compound such as cyclopentane is used as a blowing agent for a rigid isocyanurate foam, such a blowing agent has a low compatibility with an aromatic polyesterpolyol being the main polyol component, and if the amount of the blowing agent is increased, the polyester polyol and the blowing agent are likely to be separated, a foam composition before foaming tends to be non-uniform, and molding defect is likely to be observed in the molded product obtainable after foaming. If such molding defect results, no adequate heat insulating properties will be obtainable, and due to a decrease in the foam strength, the dimensional stability is likely to decrease.
To overcome such a problem, a technique has been known for improving the foam strength and the heat insulating properties by adding a specific amount of a polyetherpolyol having a high compatibility with e.g. cyclopentane. However, in order to improve the compatibility, it is required to use a polyol having a high hydroxyl value in combination, whereby the average hydroxyl value of the entire polyol component tends to be high, and accordingly, there has been a problem such that the foam density tends to be too high in a region where the isocyanate index is as high as exceeding 200.
As a method for improving the dimensional stability without increasing the foam density, Patent Documents 1 to 3 disclose a method wherein a polymer-dispersed polyol is added to a polyol component to form a rigid isocyanurate foam. Further, Patent Document 4 discloses a method wherein cyclopentane is used as a blowing agent, and potassium acetate and potassium octylate are used in combination as a nulating catalyst, to produce a rigid isocyanurate foam excellent in dimensional stability and heat insulating properties.